This invention relates to photoelectric transducer devices usable as image pick-up elements for television cameras, or as sensor elements for auto-focus systems in photographic cameras.
Recently, photoelectric transducer devices using minute photoelectric transducer elements have found their increasing use as an image pick-up element in television cameras, or as a device for AF in photographic cameras. In particular, a great number of silicon photodiodes (SPD) in an array constituting an XY assigning device, and a charge coupled device (CCD) are used as a light sensor for converting the brightnesses of the various image sections in the image plane to electrical signals in time sequence which are read out in the form of a video signal.
What has also generally been used in the past as the light sensor is the electron beam scanning type image pick-up device, for example, in the form of a vidicon type image pick-up tube having a target surface of finely-divided photoelectric particles on which an image of the object is focused while being scanned by a fine electron beam to obtain a video signal. This scanning electron beam is of almost round cross-section at the target plane. The brightness informations of the various image sections are read out by an electron beam in time sequence so as to provide outputs in the form of a video signal.
On the other hand, in order to construct a two-dimensional light sensor by the use of a solid state image pick-up device such as a CCD, it is the common practice in the prior art to configure each element in the photoelectric transducer to a square shape. These square elements all integrate the object brightnesses within the respective image-receiving surfaces and store them in the form of charges which are then sequentially read out on the basis of the self-transfer function in response to clock pulses. Thus, types of information representing the brightnesses of the various image sections corresponding to the addresses of the respective elements can be obtained as the time-sequential signals.
In this connection, it should be pointed out that, when the individual minute photoelectrical transducer elements are arranged to define the individual respective image sections, each of the minute elements converts the sum of brightness within its image receiving surface of a corresponding electrical quantity, and therefore when each minute element is square in the area as has been mentioned above, it cannot be said in a strict sense that the output of each element is, in sampling the brightness of the respective image section.
That is, in general, the "brightness information in each minute image section" essentially refers to "what is obtained by integrating the brightness while reducing the weight for the brightness value progressively from the center of the area of that image section outwards." In the case of the square photoelectric transducer elements, such weighting is neglected and instead a uniformization is crept in.
There are exceptions, however, if the objective lens for forming an image of the object on the array of these photoelectric elements has so large an aberration that the brightnesses at the various points on the object are to be distributed about the corresponding image points at the focal plane and are somewhat weighted. In this case, the error resulting from the above-described particular shape of each of the minute image sensing elements can be compensated for to some extent.
However, where the outputs from the elements, for example, between adjacent two bits to each other are compared, the use of the square element configuration can create a large gap between the output signals, because the weight in the neighborhood of the boundary between the two elements becomes larger than it actually is.
Another problem arises, for example, when two or three images of the same object are formed on respective image pick-up devices through an intermediary such as a dichroic mirror system or other suitable light splitting systems as in the color television camera. When the output signals from such plurality of image sensing devices are processed to obtain a video signal, it is required that the relative position of the photoelectric transducers be accurately adjusted, or otherwise its influence on the output signal would present itself very noticeably when no weight from the center is given in the brightness integration as in the square pattern. With this arrangement particularly when formed as a two-dimensional sensor as in a television system, since the lateral direction of the field coincides with the line scanning direction and with that in which the time-sequential signals are read out successively, the later signal treatment must be carried out by using very elaborate means, or otherwise it will be difficult to absorb the above-described error.
As for the vertical direction, since interlaced scanning is performed, the photosignals from the vertically adjacent transducer elements occur in a time gap on the order of about 1/60 second, and therefore, the buffering of the gap of signal between the upper and lower two bits becomes very difficult to achieve no matter how well the later treatment of the signals may be carried out.